Methods of manufacture of color picture tubes

ABSTRACT

TWO OR MORE SELECTED PORTIONS OR ZONES OF EACH COLOR PATTERN OF THE MOSAIC SCREEN OF A SHADOW MASK COLOR PICTURE TUBE ARE SUBSTANTIALLY SEPARATELY PRINTED IN SEPARATE PHOTOGRAPHIC EXPOSURES USING DIFFERENT OPTICAL SYSTEMS IN THE LIGHTHOUSE, TO PROVIDE DIFFERENT CORRECTIONS FOR MISREGISTER IN DIFFERENT ZONES. THE DIFFERENT EXPOSURES INVOLVE FIRST ORDER COLOR CENTER PRINTING IN ONE ZONE AND SECOND ORDER COLOR CENTER PRINTING IN ANOTHER ZONE, WITH DIFFERENT LIGHT REFRACTING CORRECTION ELEMENTS IN THE TWO EXPOSURES, EACH ELEMENT BEING DESIGNED TO CORRECT FOR MISREGISTER IN THE RESPECTIVE ZONE.

Jan. 29, 1974 I R ,H GODFREY 3,788,847

METHODS OF MANUFACTURE OF COLOR PICTURE TUBES Filed Jan. 14, 1972 I 5Sheets-Sheet 1 '1974 R. H. GODFREY METHODS OF MANUFACTURE OF COLORPICTURE TUBES Fil'ed Jan. 14, 1972 3 Sheets-Sheet 2 Fig. 3;

6' l o {1, "DISTANCE FROM CENTER OF PANEL-INCHES 4 mmmzEoEm MEEfiE Jan.29, 1974 R GQDFREY 3,788,847

METHODS OF MANUFACTURE OF COLOR PICTURE TUBES Filed Jan. 14, L972 3Sheets-Sheet :5

United States Patent 3,788,847 METHODS OF MANUFACTURE OF COLOR PICTURETUBES Richard Hugh Godfrey, Lancaster, Pa., assignor to RCA CorporationFiled Jan. 14, 1972, Ser. No. 217,785

Int. Cl. G03c 5/00 US. Cl. 96-361 9 Claims ABSTRACT OF THE DISCLOSUREBACKGROUND OF THE INVENTION This invention relates to the manufacture ofshadow mask type color picture tubes comprising a viewing faceplate onwhich is deposited a mosaic screen of systematically-arranged colorphosphor elements, such as dots or lines, a multiapertured shadow maskmounted near the screen, and means for projecting a plurality ofelectron beams through the mask to the screen.

In a conventional dot-screen color tube, three electron beams in atriangular or delta array are projected from a delta gun through a maskhaving a hexagonal array of circular apertures to a screen comprisingthree arrays of circular color phosphor dots, with each array adapted toemit light of a diflerent one of the three primary colors, red, greenandblue, and with each mask aperture associated with 'a triangular group ortriad of three different color dots. The screen may include a matrixlayer of light absorbing material, such as graphite, having amultiplicity of holes in which the color phosphor dots are deposited,for improving the contrast of the screen in ambient light.

The phosphor dots of the screen of a dot-screen color tube are usuallylaid down intrios of three dots of diifer-' ent color-emittingphosphors, e.g., red, green and blue, by a direct photographic printingprocess wherein a photosensitive coating on the faceplate is exposedthrough the apertures ofthe mask to light from a small light sourcelocated at a predetermined position relative to the mask and screen, andthe exposed coating is developed, as by washing off the unhardenedunexposed portions'of the coating, leaving the desired pattern ofexposed hardened dot portions of the coating, for one color. Thisprocess is repeated for each color, with the light source at a ditferentposition for each color. The mask may be detachably mounted on thefaceplate panel so that it can be easily removed and replaced inexactly'the same position for each exposure. In a non-matrix tube,phosphor powder may be mixed directly with the photosensitive materialin the coating, or applied to the dot portions of the coating after thelatter has been exposed, to produce the desired pattern of phosphor dotsonthe screen. The screen of a matrix color tube may be made in thefollowing manner, as described in Mayaud Pat. No. 3,558,310. The dot,portions of the photosensitive faceplate coating are exposed andhardened in three separate exposures, one for each color array, afterwhich the unexposed portions are removed, and the resulting dot patternis then overcoated with a light-absorbing coating of colloidal graphitein water which is then dried and processed chemically to remove the dotportions of the photosensitive coating and leave the faceplate coatedwith a graphite layer having the desired holes for the color phosphordots. The three color dot arrays are then photographically printed onthe screen in separate lighthouse exposures, as in a non-matrix tube, toproduce the phosphor dots in and slightly overlapping the matrix holes.

In the operation of the tube after manufacture, the electron beams aresubjected to forces such as scanning (i.e., horizontal and verticaldeflection) and dynamic con vergence (to maintain convergence of thebeams near the screen at various angles of deflection) which affect theelectron beam paths (and hence, the landing points or spots of the beamson the screen) in ways that the screenprinting light rays are notaffected. Thus, unless compensation is made for the diflerences betweenthe beam paths and the light ray paths, serious misregister of the beamspots with the phosphor dots will result, i.e., the corresponding spotand dot centers will not coincide. V

Misregister of the type wherein a trio of beam spots is shifted as aunit radially outward from the center of the screen relative to theassociated dot trio, caused by an axial shift of the deflection centersof the beams toward the screen with increasing angles of deflection, istermed radial misregister. Misregister of the type wherein theindividual spots of a spot trio are all three moved outwardly from eachother, caused primarily by dynamic convergence forces applied to thebeams resulting in lateral shifts of the deflection centers, is termeddegrouping misregister. Other types of misregister are produced by theastigmatic characteristics of beam deflecting yokes, the foreshorteningeffect of the curved screen, the beam path curvature produced by theambient magnetic fields, and the azimuthally variable distortion of thepanel-maskscreen system when the tube is evacuated.

' Radial misregister may be avoided by incorporating anaxially-symmetric radial-correction light retracting ele-, ment or lensin the light paths from the light source to the photosensitive screencoating as taught by Epstein et a1. Pat. No. 2,817,276, dated Dec. 24,1957. The effect ofthis radial lens is to move the effective location ofthe light source axially toward the screen so that at each angle to thecentral axis the ray of light appears to originate at a virtual sourcelocated at the axially-shifted or Ieffective center of deflection of thecorresponding electron eam.

Epstein et al. Pat. 2,885,935, dated May 12, 1959,

teaches the use of an aspheric axially-asymmetric lens having a singleline of symmetry in the S-plane which,

passes through the center of deflection of the beam in- 'volved and thecentral longitudinal axis of the tube, de-

In first order printing, the light printing ray and the electron beamportion for a through the same mask aperture.

Morrell and Godfrey Pat. 3,282,691 teaches the printing of color tubescreens with the light source positioned substantially at a second ordercolor center, preferably located in the same S-plane as the first ordercenter but on the opposite side of the central axis and at a particulardot on the screen pass,

distance 25 from the axis. In this case, the light printing ray and theelectron beam portion for a particular dot pass through adjacent maskapertures. This makes it possible not only to correct for most of thedegrouping error by suitably adjusting the q-spacing at each deflectionangle, but also to provide better correction for other causes of.misregister, such a fore-shortening and yoke astigmatism, by means of asuitably designed correction lens. v Herzfeld et a1. Pat. 3,476,025,dated Nov. 4, 1969, teaches the design and use of a completelyasymmetric correction lens to provide acceptable compensation at each ofa multiplicity of points distributed over the entirescreen area for allcauses of misregister. However, even with thisimproved lens, it is notpossible to obtain completely perfect register at every point on thescreen, particularly in printing screens for wide-angle (e.g., 110)color tubes, due to the necessity for blending the required elementalslopes on the lens into a smooth continuous lens surface. Usually, inphotoprinting the screen of a shadow mask tube, the photosensitivecoating is deposited on the faceplate of the panel, the shadow mask isthen mounted in the panel at a given distance q (which may be variablewith radial distance from the center) from the faceplate, and thepanel-mask assembly is placed on a lighthouse housing containing a smalllight source positioned at or near the center of deflection of theelectron beam (for the particular color being printed) of the color tubein which the panel is to be used. This center of deflection is usuallyat the mid-plane of the deflection yoke, and is spaced a distance Salong the S-axis from the central longitudinal axis of the electron gunstructure, mask and screen. The distance S is determined by the electrongun, and is related to the other parameters by the formula where q isthe spacing between the mask and the screen at the central axis, L isthe distance between the deflection plane and the screen at the centralaxis, and a is the spacing between aperture centers on the mask, toproduce equally-spaced beam spots (and phosphor dots) at the center ofthe screen. If a screen were printed under these conditions, with nocorrection lens, and incorporated in a color tube, which was thenoperated with normal scan and dynamic convergence applied, the beamspots would be registered (centered) with the phosphor dots in thecentral region, but badly misregistered at the edges.

'In Morrell Pat. 2,855,529, the degrouping portion of the misregister atthe edges is reduced by printing the screen in a single exposure, withfirst order printing, with different S and q values, for the position ofthe light source and the mask-screen spacing respectively, designed todecrease the degrouping at the outer edges, produce exact register at anintermediate region, and introduce some grouping misregister at thecenter. For example, if the measured degrouping misregister at the edgeof y, the change is S required for complete correction at the edge isThe values of q at the center and the edge to print equally spaced dots(equal size triads) is determined from & q 3S! This printing method,sometimes called a compromise S and q method, reduces the degroupingmisregister by v 4 one-half at the edge, introduces an equal amount 0grouping of the spots relative to the dots in'the center, and eliminatesdegrouping misregister at a region midway between the center and theedge. A disadvantage of this method is that it leaves the total amountof degrouping misregister between center and edge the same.

SUMMARY OF THE INVENTION A pattern of elemental areas corresponding toeach color array of the mosaic screen of a shadow mask color tube isphotographically printed in at least two stages, involving two differentexposures, using different optical systems in the lighthouse in the twoexposures, and predominantly exposing only a particular zone of thescreen coating in each exposure, in order to produce better correctionfor misregister errors in each zone. The different exposures involvefirst order color center printing in one zone, and second order colorprinting in another zone, with diflerent light retracting correctionelements in the two exposures. Each element is designed to correct formisregister in the respective zone.

The invention may be used to print either matrix or non-matrix screens,dot or line screens, and/or screens involving other than three colors.

The difierent exposures may be made with different lighthouses or with asingle lighthouse in which the light source, location, size, or shape,etc. can be changed.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side elevation view, partlyin longitudinal section of a shadow mask type color picture tube inwhich the mosaic phosphor screen is photographically printed inaccordance with the present invention;

FIG. 2 is an enlarged fragmentary rear elevation view of the mask andscreen of FIG. 1;

FIG. 3 is a plan view of the open end of the faceplate panel of FIG. 1prior to screening;

FIG. 4 is a partially broken away side elevation view of a lighthouse onwhich the exposure steps of the invention may be practiced;

FIG. 5 is a graph showing the relative brightness across the lightfields transmitted by two different light filters; and

FIGS. 6 and 7 are sketches used in explaining the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS multiaperturedcolor-selection or shadow mask 15, in

spaced substantially parallel relation to the faceplate 11, isdetachably mounted on the side wall 13 by conventional means 17. Adot-type mosaic color phosphor screen 19 is formed on the inner surface11 of the faceplate 11. A conventional electron gun structure 20 ismounted in the neck 9 for generating and directing three electron beams21 (the paths of which are shown in dashed lines) toward the mask 15.The tube is adapted to be used with conventional beam-deflecting beans,such as a magnetic yoke 23, to cause the three beams to scan the beams21 in a raster over the mask '15 and screen 19, and conventional means25 for applying dynamic convergence forces to the beams, in synchronismwith the beam scanning forces, to cause the beams to converge near thescreen at all deflection angles.

FIG. 2 shows the relation between the apertures 15a of the mask 15 andthe color dots 27 off the phosphor screen 19. Each aperture a isassociated with a triad of three dots 27, e.g. red, green and blue, asshown.

In the operation of the tube 1, at zero deflection, the three beams 21pass through centers of deflection C in the plane of deflection PP, andconverge near the screen 19. As the angle of deflection increases, theeffective plane of deflection containing the effective centers ofdeflection C moves forward (toward the screen 19) to plane P which movesall of the beam spots on the screen radially outward (from the center ofthe screen). This would cause radial misregister if the dots 27 of thescreen 19 were printed with each light source at the center C andwithout a radial correction lens. The three centers of defiection C alsomove outwardly, relative to the points C, as a result of dynamicconvergence, which causes degrouping of the beam spots in each trio ofspots associated with the same aperture 15a of the mask 15. Ideally, allof the beam spots should be exactly centered or registered with thecorresponding dots.

The present invention relates to a method of forming a pattern ofelemental areas corresponding to at least one color array of the mosaiccolor screen 19 of red, green and blue dots 27, on the inner surface 11'of the faceplate 11, by substantially separate exposures of two or morepredetermined portions or zones of the screen surface (instead of theusual single exposure of the entire surface) using first order colorcenter printing in one zone and second order color center printing inanother zone, to obtain better correction for various forms ofmisregister, in each of the zones.

For example, in FIG. 3, which shows the open end of the rectangularfaceplate panel 5 of FIG. 1 prior to screening and sealing to the funnel7, the faceplate area is arbitrarily divided into two contiguous zones,bounded by circular arcs 28, namely, a middle zone 29 and an outer zone31 constituting all of the area on each side of the middle zone 29.Preferably, the middle zone 29 extends from three-fourths to four-fifthsof the radial distance from the center to the edge of the faceplate. Themiddle zone 29 may be exposed predominantly by projecting light from asmall light source through a neutral density filter having a radiallyvariable density such that substantially only the middle zone 29 isexposed; and the outer zone 31 may be exposed predominantly byprojecting light from the same or a different size light source througha different filter having a density that varies in such manner thatsubstantially only the outer zone 31 is exposed, as disclosed in acopending application of Harry R. Frey, Ser. No. 140,345, filed May 5,1971, now U.S. Pat. 3,685,994 issued on Aug. 22., 1972, entitledPhotographic Method for Printing a Screen Structure for a Cathode RayTube. In that application, the purpose of the two separate exposures wasto facilitate printing relatively large edge dots through a mask havingapertures graded from large diameter in the center to small diameter atthe edge, without printing the dots too large in the center. The S-valueof the light source was conventional, and the same for both exposures,in the Frey application. In the present invention, the methods ofexposure are different for the two exposures, to obtain bettermisregister correction, in each of the zones.

The lighthouse 34, shown, for example, in FIG. 4, comprises a light box35 and a panel support '36 held in position by bolts (not shown) withrespect to one another on a base 37 which in turn is supported at adesired angle by lugs 38. The light box 35 is a cylindrical cup-shapedcasting closed at one end by an integral end wall 39. The other end ofthe light box 35 is closed by a plate 41 which fits in a circular recess43 in the light box '35. The plate 41 has a central hole therein throughwhich a light pipe 45, referred to as a collimator in the tube-makingart, in the form of a tapered glass rod, extends. The small end 47 ofthe collimator 45 extends slightly beyond the plate 41 and constitutesthe small light source of the lighthouse. The

larger end 49 of the collimator 45 is held in position by a bracket 51opposite an ultraviolet lamp 53. The S-value of the light source (end 47of collimator 45) may be adjusted by moving either the faceplate panel 5or the collimator 45 relative to the other. A light reflector 55 ispositioned behind the lamp 53. A lens assembly 56 is mounted on asupport ring 57 and stand-off spacers 58 by bolts 59. The support ring57 is clamped in position between base 37 and the panel support 36. Thelens assembly 56 preferably includes a correction lens 61 and atransparent filter support plate 63 held and spaced from each other by aseparate ring 65, an upper clamp 67 and a lower clamp 69. The uppersurface of the plate 63 has thereon a variable density light intensitycorrection filter 71. The filter 71 may be formed of very smallpreformed carbon particles in gelatin or other clear colorless binder,as disclosed in the Frey application. The filter has essentially aneutral gray transmittance varying only in the intensity of grayness.

In printing the phosphor screen 19 in the two zones 29 and 31 of FIG. 3,the faceplate surface 11' is coated with a photosensitive coating 72 andthen successively exposed in the lighthouse 34 (or in two differentlighthouses) using two different filters 71 in the two exposures. Onefilter 71 is designed to have a radially variable density producing alight field having a brightness such as that shown by curve 73 in FIG.5, for predominantly exposing only the middle zone 29; and the otherfilter 71 is designed to produce a light field having a brightness suchas that shown by the curve 75 in FIG. 5, for predominantly exposing onlythe outer zone 31. The total exposure at each radial distance is the sumof the two curves 73 and 75, as shown by the dashed curve 77. The twofilters should be designed so that the curves 73 and 75 cross each otherat or near the arcs 28 in FIG. 3. Preferably, the collimator tip 47 usedfor the outer zone exposure is larger than that used for the middle zoneexposure, to facilitate producing a greater exposure at the outer edgewhere the mask apertures are smaller as in the Frey application.

In this example of the invention, the dot pattern for each color in theouter zone 31 is printed predominantly only in a first exposure withfirst order color center printing, that is, with the light sourcelocated in the lighthouse at the first order color center, whichcorresponds to the center of deflection of the electron beam associatedwith the particular color dot pattern being printed. On the other hand,the dot pattern for each color in the middle zone 29 is printedpredominantly only in a second exposure (either before or after thefirst exposure) with the light source located at a second order colorcenter, preferably the one located in the same S-plane as the center ofdeflection of the tube but on the opposite side of the centrallongitudinal axis of the gun and tube, at a distance 28 from that axis,as described in the Morrell and Godfrey patent referred to above- Therelationships between beam paths and second order center light paths areshown in FIG. 3 of that patent. Each exposure should be made through alight refracting correction element or lens designed to produce the bestpossible corrections for misregister in the respective zone.

In printing the outer zone by first order printing, the compromise S andq method of Morrell Pat. 2,855,529 may be modified by choosing a maskcontour (determined by the variation in q) in the outer zone and anS-value of the light source in the lighthouse such that degroupingmisregister will be substantially completely eliminated at somearbitrary point in the outer zone, e.g., at the outer edge or corner,and designing a correction element to correct for all other misregistercauses throughout that zone, in one exposure.

An example wherein full correction is made for degrouping at the cornersof the screen, e.g., at point 79 in FIG. 3, will be described. FIG. 6shows the geometry involved, with zero and maximum deflection beam paths21 shown in dashed lines from the center of deflection C of one of thebeams. Assume the following initial conditions: L =10.5" (at center), q=.500, p =l0.0", S =.200"', R =40.7" (screen radius) and a=.0287". Ifeach color pattern of the screen were printed with the light sourcepositioned at the center of deflection C of the beam (S S =.200"), dotsin trios having a trio size (average distance of the centers of thethree dots from the center of the trio) of .010" mils) would be formed,and these dots would register with the beam spots in the operation ofthe tube at the center of the screen. However, since the effectivecenter of deflection moves forwardly and outwardly, to point C, as thebeams are deflected to maximum deflection with dynamic convergenceapplied, the beams would be badly misregistered with the phosphor dotsat the endge of the screen due to degrouping, axial misregister, etc.

Assume that the total degrouping error y, due to dynamic convergence, is.002" (2 mils) at the corners of the screen, e.g., at 55 deflection. Inthe exposure of the outer zone 31, instead of printing each colorpattern of the screen with the light source at the center of deflectionC of the beam involved, the spacing S between the light source and thecentral axis AA is increased (from S =.2O0") y to S'=.240". Thus, thelight source is placed at point C" in plane P-P in FIG. 6, to providefull correction for degrouping at the corners. Also the mask contour atthe corners is changed to make the distance L at 0=55 is determined fromthe tube geometry to be 15.01" approX.). Therefore, q=.596" andp'=l4.414", at the corners. Under these conditions, the mask will have aradii of curvature of 38.1" at the corners. The dots 27 printed at thecorners in the outer zone exposure will have a dot trio size of 10 mils(except for foreshortening distortion) and should register substantiallywith the beam spots in the operation of the tube.

The method just described could be carried out in a lighthouse with nocorrection lens 61', to compensate only for the degrouping error due todynamic convergence. However, for best results, the final screen shouldbe printed in a lighthouse incorporating at least a radial correctionlens, and preferably a continuous correction lens designed to compensatefor all errors not corrected by the modified compromise S and q methodjust described. For example, a screen can be printed as described above,without a lens, placed in a color tube, which is operated to measure theresidual misregister errors; and the results of these measurements canbe used to design a continuous correction lens 61a by any known method.This correction lens'61a can then be used in printing screens in theouter zone exposure with the modified S and q values in accordance withthe present invention.

The outer zone exposure is made through a variable density light filter71a having a brightness variation such as curve 75 of FIG. 5, to limitthe exposure substantially to the outer zone 31.

FIG. 7 shows the geometry for printing the inner zone 29 of each colordot pattern with second order printing. Two paths 21 of one beam at zeroand an intermediate deflection angle 6 are shown in dashed lines, withcenters of deflections C and C. The light source is positioned at pointC", a second order color center on the opposite side of the central axisAA from the center of deflection or first order color center C, and at adistance 28 from that axis, as shown. The exposure is made through avariable density light filter 71b having a brightness variation such ascurve 73 in FIG. 3, to limit the exposure substantially to the innerzone 29, and a light refracting correction element 6112 designed tocorrect for all misregister causes. This lens 61b may be designed andused in the manner described in Morrell and Godfrey Pat. 3,282,691. Thevalue of q, at the center of the mask and screen is determined from theformula in as,

to produce equal size beam spot trios at the center (undeflected beams).

Two outstanding advantages of second order printing are: (1) most, ifnot all, of the correction for degrouping misregister can beaccomplished merely by adjusting the mask-screen spacing q, since thespot trio and dot trio size can be changed in opposite directions by agiven change in q; and (2) the shapes of the dot trios printed aresimilar to the shapes of the astigmatically-distorted beam spot trioswhich result when a conventional magnetic deflection yoke is used toscan the beam over the screen and dynamic convergence is appliedthereto. As a result, second order printing produces better meshing ofadjacent dot trios in the central portion of the screen. However, I havefound that a second order printing has the disadvantage of being highlysensitive to both qchanges (from bogie) and changes in the aperturespacing a caused by unequal mask stretch during the mask formingoperation. Both of these changes are greatest at the outer edge of themask. On the other hand, q changes and mask stretch present very littleproblems in first order printing. For these reasons, I have used secondorder printing in the inner zone, to obtain better spot-dot register andgood meshing, and first order printing in the outer zone, where secondorder printing has disadvantages. The inner zone also includes thecritical minor axis where first order correction lenses cannot cope withthe beam spot trio distortions brought about by yoke astigmatism,particularly in a dual-lens-source system.

Instead of limiting the second order printing to the inner zone 29, theentire screen may be printed with second order printing in one exposurewithout the filter 71a, with the outer zone printed with first orderprinting in a separate exposure with the filter 71b to provide a fill,thus distorting the finished phosphor dots in such a way that full beamspot landing on the dots is achieved in spite of the dot location errorsproduced by mask stretch and/or q errors in the outer zone.

Although the invention has been described in connection with anon-matrix dot screen color tube, it will be understood that theinvention can also be used to print each color pattern of a matrix dotscreen tube, or a linescreen tube of the shadow mask type, with orwithout opaque guard bands between the phosphor lines.

I claim:

1. In the manufacture of a shadow mask picture tube having a mosaiccolor phosphor screen including an array of discrete phosphor elementsdisposed on a support, all of which are adapted to emit light of a givencolor, a multi-apertured shadow mask, and means for projecting anelectron beam through said mask to said screen; the method of layingdown said array on said support, comprising the steps of:

(a) photographically printing on said support the pattern of said arrayof phosphor elements predominantly in a first zone of said array, saidfirst zone including a middle portion of said array, including exposingsaid first zone from a first light source, positioned substantially at asecond order color center for said array, and refracting the exposurelight through a first continuous light refracting correction element;and

(b) photographically printing on said support the pattern of said arrayof phosphor elements predominantly in a second zone of said array saidsecond zone including outer portions of said array including exposingsaid second zone through apertures of said shadow mask from a secondlight source, positioned substantially at the first order color centerfor said array, and retracting the exposure light through a secondcontinuous light retracting correction element; the surface contours ofsaid two correction elements being diiferent, each of said correctionelements being designed to minimize misregister between the beam spotsand the phosphor elements in the operation of said tube. 2. In themanufacture of a color picture tube having a mosaic color phosphorscreen comprising a plurality of arrays of discrete phosphor elements,the elements of each array being adapted to emit light of a diiferentcolor, an apertured shadow mask spaced from said screen, and means forprojecting a plurality of electron beams, one for each array, throughthe apertures of said mask and onto said screen; the method of layingdown one of said arrays of elements on a screen support by a directphotographic process, said method comprising the steps of:

(a) applying to said screen support a coating comprising aphotosensitive binder; (b) exposing at least a first zone of saidcoating through said mask apertures to light from a first relativelysmall light source positioned substantially at a second order colorcenter for said one array and retracting the exposure light through afirst continuous light retracting correction element interposed betweensaid light source and said mask; exposing predominantly only a secondzone of said coating through said mask said first zone including amiddle portion of said coating; apertures to light from a secondrelatively small light source positioned near the first order colorcenter for said one array and retracting the exposure light through asecond continuous light refracting correction element interposed betweensaid second light source and said mask said second zone including anouter portion of said coating; and ((1) then developing said exposedcoating to produce a pattern of exposed portions of said coatingcorresponding to said one array of elements on said screen support; thesurface contours of said two correction elements being different, eachof said correction elements being designed to minimize misregisterbetween the beam spots and the phosphor elements in the operation ofsaid tube.

3. The method of claim 2, wherein the entire surface of said coating isexposed in step (b).

4. The method of claim 2, wherein predominantly only said first zone isexposed in step (b).

5. The method of claim 4, wherein said first zone is a middle portion ofsaid coating, and said second zone is made up of the two outer portionsof said coating on each side of said middle zone.

6. The method of claim 5, wherein the boundaries be tween said zones arelocated at three-fourths to four-fifths of the distance between thecenter and the outer edge of said screen support.

7. The method of claim 1, wherein said screen support has a longitudinalaxis perpendicular thereto at its center, and said second order colorcenter is the one that is on the opposite side of said axis from saidfirst order color center.

8. The method of claim 2, wherein said mosaic screen comprises threehexagonal arrays of color phosphor dots, and said means is adapted toproject three electron beams in a A-array onto said screen.

9. The method of claim 2, wherein said coating includes a color phosphormaterial, and said exposed portions of said coating constitutes said onearray of elements.

References Cited UNITED STATES PATENTS 3,685,994 8/1972 Frey 9636.13,476,025 11/1969 Herzfeld 1 3,672,893 6/1972 Robinder et a1 9636.13,222,172 12/1965 Giuffrida 96-36.], 2,733,366 1/1956 Grimm et al.96-36.1

NORMAN G. TO'R'CHIN, Primary Examiner -E. C. KIMLIN, Assistant ExaminerUS. Cl. X.R. 951

